VEHICLE POWER SUPPLY DEVICE

A vehicle power supply device includes an in-vehicle battery mounted on a vehicle, a backup power supply as a spare of the in-vehicle battery, a motor that drives an in-vehicle electric device by being supplied with electric power from the in-vehicle battery or the backup power supply, a charger that charges the backup power supply by supplying the electric power from the in-vehicle battery to the backup power supply, an in-vehicle battery voltage acquirer that acquires an output voltage of the in-vehicle battery, and a controller that controls the charger, in which when the output voltage of the in-vehicle battery becomes less than a first voltage, the output voltage being detected by the in-vehicle battery voltage acquirer, the controller charges the backup power supply so as to output a second voltage with which the motor is at least operable.